Month: May 2012

Genetic determinism, according to Wikipedia, is the belief that genes, along with environmental conditions, determine morphological and behavioral phenotypes. It does not mean that genes totally rule, and will decide your preferred political party, your religion, and your love of carrots. It just means that genes are really important in shaping who you are.

So how much is decided by genes, and how much by environment? How much nature and how much nurture? Studies of identical twins have helped us answer this question. Identical twins are the result of an early split of an embryo, thereby giving two people instead of one, but with exactly the same set of genes.

Below is a picture of my grandmother, Martha, and her identical twin Mary. In the small town where they grew up they were known as the Sin Twisters. No one could tell them apart. They’d often swap out for taking tests in high school, and even on dates. And no one was the wiser. Shades of the movie The Parent Trap, but they turned out better than Lindsey Lohan.

So, give two people the same set of genes and they’ll look pretty much identical. It is easy to conclude that genes are extremely important in determining appearance. But what about other things, like intelligence, athletic ability, and health? Twins can also help us figure out the genetic contribution for these features. The key is to study twins that were for some reason separated at birth and raised in different environments. If genes are really important in defining characteristics then one would predict that identical twins raised by different families would still show significant similarities, above and beyond their physical appearance.

Sir Francis Galton was the first to use twins to study the genetic contribution to traits. He was a cousin of Charles Darwin’s and was very much taken by the theory of evolution and interested in studying the inheritance of characteristics, including intelligence. He coined the term “nature versus nurture” and concluded from his work that nature was more important than nurture.

The modern day Minnesota Twins Study is one of the most comprehensive investigations of nature versus nurture. They have analyzed hundreds of identical and fraternal twins, raised in the same or different environments. It turns out that environment has relatively little effect on physical features. If you take identical twins and rear them apart they still look identical. And if you take fraternal twins and raise them together they still don’t look the same, although there will be similarities, in part because they do share half of their genes.

IQ also showed strong heritability, with the results indicating that about 70 to 80 percent of a person’s IQ is determined by genes. There were also some surprising results to come from the study, showing genetic contribution to unexpected psychological attributes. For example, there seem to be happy and sad genes. Identical twins, even when raised apart, scored more alike in measures of happiness than fraternal twins. And another surprise was the connection between genes and the level of religiosity. One might think that family environment in this case would be particularly important, with children exposed to religion on a weekly basis much more likely to become religious. But if one identical twin was religious, then the other was more likely to be as well, even when raised separately. Of course genes did not pick the faith. One twin might be a devout Protestant, while the other twin, raised by a different family, would be a devout Jew. And what about health? Genes are clearly important here as well, with hundreds of diseases now known to have a genetic component.

Of course genes are also important in defining our athletic ability. As an example of the relationship between genes and athleticism consider the dogs shown below. They are both female whippets of about the same age. But one has a mutation in the myostatin gene, and as a result her muscles have grown to rather enormous proportions. She is one very strong and very fast whippet. It turns out that some human body builders have natural occurring mutations in the same gene. They were born to body build.

So genes play an important role in defining both our physique and our psyche. But it is also important to note that they don’t completely define us. Identical twins are certainly similar, but they are not the same. Although our genes establish limits, within those limits there exist a wide range of possibilities, determined by chance and our environment.

Finally, there is the question of how much we currently understand about the relationship between genes and traits. Suppose that we could completely control the genetic makeup of our offspring. Perhaps shockingly, this possibility is not as far-fetched as you might think. Could me create children that are incredibly smart, healthy, good looking and athletic? The truth is that right now we understand very, very little about the genetic equations that define these traits. And it is clear that the answers are going to be, in general, extremely complicated.

But there is currently a revolution going on in the world of DNA sequencing. The price continues to plummet. We are now sequencing the DNAs of tens of thousands of people, and in the near future it will be millions. We will then be able to connect the dots, and relate the different orders of the G,A,T,C bases to the different traits of the people that carry them.

The future of our species could get very interesting.

About the Author: Eveloce was an undergraduate at UCLA, received his PhD from the University of North Carolina at Chapel Hill and was a postdoctoral research fellow at Harvard Medical School. He has published over one hundred research articles, co-authored the third edition of the medical school textbook Larsen’s Human Embryology, and serves on the editorial board of the science journal Developmental Biology. He wrote the book “Designer genes: A new era in the evolution of man” published by Random House and available at Amazon.

The 24 year old graduate student Aimee Copeland fell when a homemade zip line over the Little Tallapoosa River broke. She hit the rocks below, suffering deep cuts that became infected with flesh eating bacteria. And the horror began, with doctors forced to amputate both feet, both hands, all of one leg, and part of her body, in an effort to save her life. When told they would remove her hands she reportedly looked up and mouthed the words “Let’s do this”, appreciating that her purple hands would have to go.

So, what is flesh eating bacteria? The condition can be caused by many different kinds of bacteria, including Streptococcus pyogenes, Staphylococcus aureus and Clostridium perfringens. In the case of Aimee the culprit appears to be Aeromonas hydrophila, found in warm climates and fresh or brackish water. Like the antibiotic resistant strains of Staphylococcus aureus (MRSA), it is resistant to most antibiotics. It produces a toxin (poison) called Aerolysin Cytotoxic Enterotoxin that damages tissue.

How do you catch it? It can infect cuts, as was the case for Aimee, or you can even get it from a bruise (about one third of cases), and sometimes there is no evidence of an injury at all. You can also get it through foods, including seafood, meats and some vegetables.

The bacteria that cause it are fairly common, so the question is why do some people get it and others not? People with compromised immune systems are susceptible, as you might expect. But there is also increasing evidence that some people are genetically predisposed to get certain infections, even if their immune systems are otherwise perfectly fine. For some reason their immune systems are particularly prone to invasion by certain strains of bacteria. It also appears that the bacteria can make toxins that disable the immune system.

How do you treat it? The Aeromonas bacteria encode a protein called beta lactamase that degrades penicillin and the penicillin derivative antibiotics. Despite antibiotic resistance most strains will respond to so-called third generation agents. The other treatment is surgical removal of the most infected areas (surgical debridement).

What are the symptoms? The first symptom is usually pain at the site of a wound. Then the pain gets worse and the tissue around the wound swells and can change in color. As the infection spreads there are flu like symptoms with fever, nausea and diarrhea. It is important to get treatment early. Death can result within 24 hours, and even with high-dose antibiotic treatment about 25% of patients die.

The technical term for flesh eating bacteria is necrotizing fasciitis, which is a fancy way of saying dying tissue. It is generally relatively rare, with about 4 cases per 100,000 people (http://www.bioedonline.org/news/news.cfm?art=1234). So don’t panic, but be careful!

So maybe Count Dracula had it right after all. It looks like that young blood has some really good stuff in it. The lab of Tony Wyss-Coray at Stanford has been studying the causes of the aging of the brain. As baby boomers get older and older they get more and more interested in how to keep their brains young.

The Wyss-Coray lab used parabiosis to see if there might be something in the blood that regulates brain aging. Parabiosis is a surgical technique that connects the circulatory systems of two mice. It is sort of like taking two mice and turning them into Siamese twins. Sorry mice, I’m sure it is no fun, but it is for the sake of science. For controls they connected young mice to young mice, and old mice to old. Not surprisingly, nothing much happened.

But when they connected young mice to old mice, Eureka! The brains of the old mice started behaving like they were much younger! The brain stem cells, which normally slow down in old mice, became active and divided more. Neurogenesis, the formation of new neurons, was kicked back on in the old brains. The reverse effects also took place in the young mice receiving old blood. Their cognitive functions declined, as measured by performance on maze tests, and by studies of their synaptic plasticity.

Was the active element in the shared blood cells or plasma? To test this they injected old plasma into young mice and vice versa. They found that the plasma was sufficient for the brain effects, so cells were not necessary. Then they examined the plasma carefully to better define the differences in young and old. They found a cytokine, CCL11, which elevates in concentration in both old mice and people. When they injected CCL11 into the blood of young mice it was able to cause aging effects very similar to that of old blood.

So, if you have a young brain and want an old one, they have the answer. Shoot up some CCL11. But, if you have an old brain and want a young one, the more likely scenario, they still are not sure what to do. Perhaps inactivate your CCL11, maybe with antibodies? They don’t describe this experiment, but it would seem a possibility. Or wait until they discover the active ingredient in the young blood that provides the neuronal fountain of youth? Or hunt the night for beautiful young women, so you can drink their blood?